How Do You Test a Miniature Circuit Breaker?

How Do You Test a Miniature Circuit Breaker?


In this post, I am going to talk about Miniature Circuit Breaker testing.

The purpose is to help YOU ensure the reliability of the miniature circuit breaker.

We’ll discuss testing procedures and why MCB testing is important.

Plus: The benefits of testing the MCB.

Also, I’ll tell you exactly how do you test a mini circuit breaker.

Let’s look right in.

How do you test a mini circuit breaker?

You can test Mini circuit breakers using different types of testing equipment and test techniques.

Testing circuit breakers is rather challenging than testing other electrical tools.

Why so?

That’s because the short circuit current flows in a larger amount and carries greater hazards.


Testing of mini circuit breakers is divided into two groups mainly.

  1. Type tests
  2. Routine tests

But before I give an in-depth overview of circuit breaker testing categories, do you know what actually the Miniature Circuit Breaker Test is?

So, first thing first…

“An MCB test aims to examine the trip time characteristics of the MCB – whether it’s in the limit or not, and checks the availability of the MCB’s auxiliary contact.”

Why is Testing Mini Circuit Breakers Important?

Think mini circuit breakers are safety tools, and they’ll perform their action when needed, then why get into hectic testing?

Think again. What if the malfunction occurs and the safeguarding gadget – your mini circuit breaker you have put your all trust into – is out of order?

The malfunction can damage your expensive electric pieces of equipment.

Also, it can put your life and those living with you in danger.

Seems like a nightmare!

A circuit breaker can laze for years. But it has to be responsive right at the moment electrical fault occurs. That too in milliseconds!

Therefore, MCB testing holds vital importance.

Perform a quality check first. Then, you need to execute on-field testing during installation.

Later on, regular maintenance and frequent testing ensure the safety and reliability of its performance.

So, testing the performance of your mini circuit breakers regularly goes without saying.

After all, you can’t compromise the well-being of your electronics and your family.

Can you?

With that said, now, I’d head towards a detailed breakdown of the MCB testing categories.

Want to dig deep into the inside information? Go on!

4 Type Tests of MCBs Carried Out in the Labs

Type tests are conducted in specifically built test laboratories. The purpose of the type tests is to prove the capabilities and rated characteristics of the MCBs.

Further classification of type tests are:

#1. Mechanical Test:

This test examines the mechanical capability of the breaker involving the opening and closing of the breaker. If the circuit breaker opens and closes at the correct speed along with performing its duty and operation without mechanical failure, it qualifies for the test.

#2. Thermal Test:

The thermal test looks over the thermal behavior of the circuit breaker. The circuit breaker under examination tackles the temperature rise – due to the flow of its rated current.

For a current less than 800A, the temperature must not exceed 40°.

And, for the normal value of current – 800A and above, the temperature should not surpass 50°.

#3. Dielectric Test:

This test tries out the power frequency and impulse voltage withstanding capacity of the circuit breakers.

Power Frequency test is employed on a NEW circuit breaker.

On the other hand, the voltage test varies with a circuit breaker rated voltage.

You can take on the voltage test within a frequency range of 15-100Hz.

This test can be applied:

  1. Between poles with closed-circuit breaker
  2. Between poles and earth with open circuit breaker
  3. Across terminals with open circuit breakers

In impulse tests, an impulse voltage of a specified magnitude is applied to the circuit breaker.

In the case of outdoor circuits, dry and wet tests are also carried out.

#4. Short-circuit Test:

This test is taken to know how the circuit breaker will react if a short-circuit fault occurs. The circuit-breaking undergoing trial is exposed to sudden short-circuits.

Afterward, an Oscillogram records the behavior of the circuit breaker at the time of:

  • Switching in
  • During contact breaking
  • After arc extinction

A Sneak-Peek into the Lab Test of Mini Circuit Breaker

During testing, the MCB under evaluation is disconnected from the circuit and connected to a test set.

The test set produces different current ratings to simulate load conditions and fault currents.

The short circuit tripping element is tested first.

The overload tripping element is tested next.

A stability test with nominal current completes the tests for the MCB.

When an MCB qualifies for the test, the same process is repeated with the other.

8 Routine Tests of MCBs to Ensure their Performance

Routine tests are not lab tests. These tests are conducted at the manufacturers’ end.

These tests confirm the proper functioning of circuit breakers, routine maintenance, for instance.


Verifying that the performance of the circuit breaker conforms to the manufacturer’s calibration curves.

Routine tests are free from the hassle of complex gear.

All you need to act upon are some guidelines and recommendations.

Here is the list of some of the routine tests:

#1. Primary Inspection and Testing:

The dirt and debris around can accumulate in the circuit breaker and can affect its operation. However, disposing of that accumulation off is easier.

Flip the breaker’s lathe from the ‘On’ position to ‘Off’ and clear away the dust. Simple!

Don’t forget to put the lathe back to the ‘On’ position afterward.

#2. Circuit Breaker Trip Test:

You can determine the mechanical or electrical issues by analyzing the current trip coil consumed during the circuit breakers’ operation.

#3. Insulation Resistance Test:

This test verifies the appropriate functioning of the insulating material that makes up the molded case breakers.

For insulation resistance testing, an instrument called Megger is used.

#4. Connection Test:

Connection testing ensures that a suitable electrical connection is available. It also looks for traces of overheating.

#5. Overload Tripping Test:

This test is performed by inputting 300% of the breaker rating into each pole of the circuit breaker.  The purpose is to check whether the circuit breaker will operate or not.

Hot tip: Always carry out this test after consulting the manufacturer’s manual of the MCB!

#6. Instantaneous Magnetic Tripping:

Instantaneous Magnetic Tripping test finds out that the magnetic tripping feature is functional or not.

#7. Power Frequency Overvoltage Test:

This test verifies the capability of a CB while confronting overvoltage conditions of all types without compromising the economical aspects of manufacturing.

#8. The Millivolt Drop Test:

The millivolt drop test determines the voltage drop within the current path of the breaker mechanism.

Caution! You must perform routine tests under stable conditions and a suitable temperature to avoid variations in the data and ensure safety.

4 Ways Routine Testing of Mini Circuit Breaker is Performed

#1. Testing with a Circuit Breaker Analyzer

The way to test a circuit breaker with a circuit breaker analyzer depends on the type of possible problem you want to confirm.

CB Analyzer checks the opening or closing time of each pole in single or combined operations (O, C, O-C, C-O, O-C-O, C-O-C).

Additionally, it checks the possible difference between poles or mismatch time which may lead to a dangerous lack of synchronism.

That further leads to checking other features like the possible bouncing, the coils condition, the proper performance of the pre-insertion resistance, the mechanical analysis through contact travel speed, and acceleration data using the appropriate transducers.


#2. Testing with a Micro-ohmmeter

Resistance testing with Micro-ohmmeter is a way of testing a circuit breaker for avoiding and identifying the forthcoming issues.

Such testing requires reliable measurements and a high-power wide injection range. These regimens ensure longer test leads, fewer connection problems, and more accurate measurements.

#3. Testing with a High-Current Primary or Secondary Injection Tester

LV type circuit breakers and molded case circuit breakers are tested using Primary injection.

However, mini circuit breakers are tested using secondary injection test sets. Circuit Breaker secondary injection testing is a substitute to the standard Primary Injection Testing.

#4.  Testing with a Multimeter

A Multimeter is the most efficient way to test circuit breakers. It can measure volts, amps, and ohms through outlets, fixtures, and breakers.

In this test, one prong of the Multimeter is touched with the breaker’s terminal screw, and the other prong is touched with a ground screw. The ground screw is located in a metal bar on the right-hand side of the electrical panel.

Once these prongs are attached, check the reading. If the reading is zero, the breaker has malfunctioned.

Step-by-Step Procedure for Connection Testing a Mini Circuit Breaker

Before you run such a test, you must be aware of some features of the MCB.


  • How does it work?
  • Its type
  • Its current tolerance rate

Required Testing Tools:

  • An MCB – to test
  • Sverker – used as a current source

Let’s Get Testing!

Step 1: First, visually inspect the breaker.Check for:

  • The tightness of all wires
  • Wire ferrules
  • Physical damage or defect – if there’s any

Once you are done with the visual inspection, you are all set to start the performance test.

Step 2: Connect Sverker to the MCB switch directly.

Step 3: Inject from Sverker twice of its rated current and measure the trip time.

Step 4: Compare the trip time with the limit defined in the MCB’s manual based on its type.

Auxiliary contacts must be checked in both conditions of MCB: Open and Close.

10 Benefits of Routine Testing Mini Circuit Breaker

  1. The testing procedures are quick and easy to perform on-site.
  2. You can perform on/offload circuit testing.
  3. You can test the performance of the whole tripping cycle.
  4. You can determine the overall timing of the tripping system.
  5.  Identifying whether the circuit breaker needs maintenance or not becomes easier.
  6. Routine testing is a part of a comprehensive diagnostic maintenance program.
  7. It indicates the possible problems beforehand and helps you avoid potential issues.
  8. It’s a cost-effective protection measure and increases the life of your safety tools.
  9. Routine testing aids you in building up a test record database.
  10. It assists you to spot the bad characters in your circuit breaker panel.

3 Tips to Visually Test the Quality of MCB before You Buy

I have already talked about the lab testing and factory testing of the MCBs.

In this section, I want to throw a little light on the quality testing of the mini circuit breakers to help the BUYERS!

This testing is way different from the routine tests and final confirmation checks. Here are a few tips.

#1. Watch for the appearance.

Plastic parts of the MCB should be clean and without damage. Such as, there must not be any cracks and air bubbles on the surface. Furthermore, the anti-corrosion coating of metal parts must be glossy and free of pinholes, dots, and bubbles.

The juncture has to be flat and aligned. And, the rivets must be tightly fixed.

#2. Inspect the main material of the MCB’s case.

Nylon is the material used for the casing of the MCBs. Normally, PA66 and PA6 polymers of Nylon.

Nylon PA66 is a better choice than PA6 for its higher flame resistance, brighter color, and outlasting life.

#3. Check for coil and wire material and its thickness.

The coil and wire of the MCBs are made up of red copper. Different coils are employed for different ratings. Coils of 1.13mm*10 for 10A, and 2.4mm*5mm*2 for 63A!

Some manufacturers can use alternative materials to reduce their costs. Such as brass and iron. You can judge brass with the color difference. Iron can be identified with the help of a magnet.  

After you confirm the coil and wire material, next comes the thickness check.

You can measure the thickness to ensure its compliance with the current rating you want it to endure.

Besides, you can also carry out a mechanical operation test and performance inspection of the random items from your batch. And decide does the batch qualifies your quality inspection or not. 


There you have it. Different mini circuit breaker testing categories, testing procedures, the significance, and benefits!

Now, I’d like to hear back from you.

Testing a mini circuit breaker isn’t a task everyone can do. However, it doesn’t require many tricks to run a visual quality test on a mini circuit breaker before you invest in it.

Have you ever tested a mini circuit breaker? If so, how did it go?

Or maybe you want to know something more!

Drop your queries and your visual test experiences in the comments below.


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